Tests: Add a SILGen test for async functions with the @_backDeploy attribute.

Author: tshortli

test/SILGen/back_deploy_attribute_async_func.swift

@@ -0,0 +1,58 @@
+// RUN: %target-swift-emit-sil -parse-as-library -module-name back_deploy %s -target %target-cpu-apple-macosx10.50 -verify
+// RUN: %target-swift-emit-silgen -parse-as-library -module-name back_deploy %s | %FileCheck %s
+// RUN: %target-swift-emit-silgen -parse-as-library -module-name back_deploy %s -target %target-cpu-apple-macosx10.50 | %FileCheck %s
+// RUN: %target-swift-emit-silgen -parse-as-library -module-name back_deploy %s -target %target-cpu-apple-macosx10.60 | %FileCheck %s
+
+// REQUIRES: OS=macosx
+// REQUIRES: concurrency
+
+@usableFromInline func otherFunc() async {}
+
+// -- Fallback definition of asyncFunc()
+// CHECK: sil non_abi [serialized] [ossa] @$s11back_deploy9asyncFuncyyYaFTwB : $@convention(thin) @async () -> ()
+// CHECK: bb0:
+// CHECK:   [[FNREF:%.*]] = function_ref @$s11back_deploy9otherFuncyyYaF : $@convention(thin) @async () -> ()
+// CHECK:   [[APPLY:%.*]] = apply [[FNREF]]() : $@convention(thin) @async () -> ()
+// CHECK:   [[RESULT:%.*]] = tuple ()
+// CHECK:   return [[RESULT]] : $()
+
+// -- Back deployment thunk for trivialFunc()
+// CHECK-LABEL: sil non_abi [serialized] [thunk] [ossa] @$s11back_deploy9asyncFuncyyYaFTwb : $@convention(thin) @async () -> ()
+// CHECK: bb0:
+// CHECK:   [[MAJOR:%.*]] = integer_literal $Builtin.Word, 10
+// CHECK:   [[MINOR:%.*]] = integer_literal $Builtin.Word, 52
+// CHECK:   [[PATCH:%.*]] = integer_literal $Builtin.Word, 0
+// CHECK:   [[OSVFN:%.*]] = function_ref @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:   [[AVAIL:%.*]] = apply [[OSVFN]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:   cond_br [[AVAIL]], [[AVAIL_BB:bb[0-9]+]], [[UNAVAIL_BB:bb[0-9]+]]
+//
+// CHECK: [[UNAVAIL_BB]]:
+// CHECK:   [[FALLBACKFN:%.*]] = function_ref @$s11back_deploy9asyncFuncyyYaFTwB : $@convention(thin) @async () -> ()
+// CHECK:   {{%.*}} = apply [[FALLBACKFN]]() : $@convention(thin) @async () -> ()
+// CHECK:   br [[RETURN_BB:bb[0-9]+]]
+//
+// CHECK: [[AVAIL_BB]]:
+// CHECK:   [[ORIGFN:%.*]] = function_ref @$s11back_deploy9asyncFuncyyYaF : $@convention(thin) @async () -> ()
+// CHECK:   {{%.*}} = apply [[ORIGFN]]() : $@convention(thin) @async () -> ()
+// CHECK:   br [[RETURN_BB]]
+//
+// CHECK: [[RETURN_BB]]
+// CHECK:   [[RESULT:%.*]] = tuple ()
+// CHECK:   return [[RESULT]] : $()
+
+// -- Original definition of trivialFunc()
+// CHECK-LABEL: sil [available 10.52] [ossa] @$s11back_deploy9asyncFuncyyYaF : $@convention(thin) @async () -> ()
+@available(macOS 10.51, *)
+@_backDeploy(before: macOS 10.52)
+public func asyncFunc() async {
+  await otherFunc()
+}
+
+// CHECK-LABEL: sil hidden [available 10.51] [ossa] @$s11back_deploy6calleryyYaF : $@convention(thin) @async () -> ()
+@available(macOS 10.51, *)
+func caller() async {
+  // -- Verify the thunk is called
+  // CHECK: {{%.*}} = function_ref @$s11back_deploy9asyncFuncyyYaFTwb : $@convention(thin) @async () -> ()
+  await asyncFunc()
+}
+